The benefits of insulation

Nersa recently announced that it had approved only 9,4% of the 16% consumer electricity cost increase that Eskom had applied for. Eskom has since threatened to discontinue using its diesel generators, while carefully sidestepping the root cause of the energy crisis: the fact that the new Medupi and Kusile power stations are years behind schedule.

With the threat of load-shedding once more with us, it seems opportune to talk about saving power.

I’ve always stressed that a kilowatt hour not used is a kilowatt hour saved. Between 20% and 30% of energy consumed by buildings is wasted. Some of this may be unavoidable, but a large portion of this can be eliminated with good practice, and without spending much.

The heat transfer through a wall, roof or pipe is defined by the equation below, where Q is the heat transfer per metre squared, Tout is the outside temperature, Tin is the indoor temperature, and R is the thermal resistance value:

For a tiled roof, the R1 value is 0,091. The inside surface value (R2) is 0,44, and the outside surface area value (R3) is 0,05. The total heat transfer rate is thus 17,2W/m2:

However, if mineral wool insulation (R4=11) is installed in the roof, the heat transfer rate reduces to 0,86W/m2. In a 250m2 house, this difference equates to a 4,1kW air conditioner:

Consumers are often advised to switch off their geysers to save power. This is only true in specific circumstances. A geyser’s heat is controlled by the thermostat. As the geyser loses heat, the thermostat causes the element to reheat the water in order to maintain the temperature. If the geyser is not switched off, this process will occur several times a day. If it is switched off, it will occur only once (when the geyser is switched back on), but over an extended period. Total electricity consumed will be roughly the same.

It is far more efficient to stop the geyser from losing heat by improving insulation. Wrap the geyser and all visible pipes in insulation, using cheap blankets, seed bags, feed bags or rubber. If a pipe feels warm, it is expending energy and should be wrapped. This reduces heat loss and prevents electricity wastage.

Similarly, a hot water tap dripping at, say, 30 drips/minute, wastes about 10l/ day. This means 300l/month, which requires 17,5kWh to heat to 65°C. At R1,93/ kWh, this equals R33,78/month, or R405/ year. While this seems insignificant, a new washer costs only R5, thus saving you R400/year.

Agribusiness and farming The principle of insulation and energy waste applies to several activities. In abattoirs and dairies, where large volumes of hot water are used, significant energy is wasted due to poor insulation and water management. In an abattoir, for example, the leak might not be 10l/day, but 1 000l/ day, adding up to R3 300/month.

The same principle applies to cooling systems. If coolant lines are poorly insulated, energy is lost through pipe walls. If a coolant line is sweating or dripping, electricity is being wasted. Insulating the pipe results in a more efficient cold room and lower electricity consumption.

To sum up, the key to reducing cost lies in good management. For example, while an energy-efficient lightbulb obviously cuts down on power usage, it cannot prevent wastage if it’s left on when it should be off. This is an operator problem, not an equipment problem.

Equally, while a brand-new heat pump uses less power than an electric boiler, this applies only when both are switched on. When they are both switched off because everything is well insulated and retaining heat, neither will use any energy.